British patent specification No. 2,111,478 relates to tumor inhibiting indole derivatives of the formula ##STR3## wherein R.sub.1 is hydrogen, a hydroxy group or a C.sub.2 -C.sub.6 alkanoyloxy group, R.sub.2 is hydrogen, a hydroxy group, a C.sub.2 -C.sub.6 alkanoyloxy group or a halogen atom, R.sub.3 is a C.sub.1 -C.sub.6 alkyl group, R.sub.4 is hydrogen or a C.sub.1 -C.sub.6 alkyl group, R.sub.5 is a hydroxy group or a C.sub.2 -C.sub.6 alkanoyloxy group, R.sub.6 is hydrogen or a halogen atom and R.sub.7 is hydrogen or a halogen atom.
Furthermore, tumor inhibiting ethylene diamine-platinum (II) complexes are known, wherein a CH.sub.2 group of the ethylene diamine is substituted by a benzyl radical, phenylethyl radical, thienylmethyl radical, indolylmethyl radical or imidazolylmethyl radical (German patent specification DE-OS No. 36 05 191) or wherein both CH.sub.2 groups of the ethylene diamine contain a phenyl radical or a substituted phenyl radical (German patent specifications DE-OS Nos. 34 05 611; DE-OS 36 04 866).